Convex upper platen for a pulp press



Nov. 13, 1962 e. E. LAMB CONVEX UPPER PLATEN FOR A PULP PRESS Filed Jan.18, 1960 INVENTOR. GEORGE E. LAMB M 2 HTTOEN 5 This invention relates topresses as used in the paper pulp manufacturing industry. Morespecifically stated, the invention relates to improvements in pressesthat are especially designed for the compressing of chemical cellulosepulp bales in order to increase the density of the pulp and to decreasethe thickness of space occupied by the bale; the latter being in orderthat a more favorable ocean freight rate may be obtained where rates arebased on the space occupied by the freight rather than on its weight.

Explanatory to the various objects and advantages of this invention, itwill here be pointed out that the manner of pressing a paper grade pulpbale is quite important for various reasons well known in the industry.A press, designed to properly press chemical cellulose bales, must becapable of applying a very light cornpressing pressure, or a highpressure s-uflicient to dead press the bale. In a modern, high speedfinishing room, the press generally limits the production rate. Thecycle of the press and the retention period allowed for escape of airfrom the pulp bale under compression will determine the number ofpresses required to obtain a desired production. The retention periodmust be reduced as much as possible in order to get the shortestpressing cycle. During the last twenty years the retention period hasbeen reduced from approximately 60 to approximately seconds, by reasonof utilizing increased press pressures but the using of increasedpressures has resulted in production of a greater percentage of stickersand also has necessitated the installation of vacuum breaker plates onthe upper press platens in order to prevent, in the opening of thepress, the-lifting of the bale from the lower platen and an incidentdropping of the lifted bale when the vacuum breaks.

The pressing of bales of dry pulp, especially at high speeds, involves anumber of factors not ordinarily found in other pressing operations. Forexample, a pulp bale exerts a constantly increasing resistance tocompression as the pressing progresses and also, by reason of springback of the bale, exerts high but decreasing pressures on the press overa considerable distance as the press opens. The closing rate of aproperly designed pulp press will decrease as the press pressureincreases, so as to utilize the full power of the pulp motor over theentire closing cycle and the press must have an adequate means ofdecompressing the bale.

In view of the foregoing explanatory matter, it has been the principalobject of the present invention to provide an improved form of pressplaten for a pulp press, incorporating therein, certain novel vacuumbreaking and design features whereby the present retention period fordissipation of air from the bale being pressed may be further reduced.

It is a further object of the present invention to provide a pressplaten with a bale engaging surface of novel contour that, in use of theplaten, in bale pressing, avoids the trapping of air in the bale undercompression and expedites air exhaustion therefrom. Furthermore, it isan object of this invention to so design the bale contacting surface ofthe platen that the compression of the bale progresses from the insideareas to the outside areas thereby bringing about a faster outflow ofair from the bale and avoids compression of pulp fibers about thePatented Nov. 13., 1962 2 outer edge surface of the bale and thuspermits easier flow of air within and its outflow from the bale.

Yet another object of the invention resides in the provision of animproved press platen, embodying the objects and advantages aboverecited, whereby under controlled pressures a perfectly flat top surfacemay be pro duced on the pressed and finished bale without lengtheningthe retention period.

In accomplishing the above mentioned and other ob jects of theinvention, I have provided the improved details of construction, thepreferred forms of which are illustrated in the accompanying drawings,wherein:

FIG. 1 is an elevation of a typical pulp bale press equipped, with apress platen embodying the improvements of the present inventiontherein.

FIG. 2 is an enlarged sectional View of the platen, taken on line 2-2 inFIG. 1.

FIG. 3 is an enlarged sectional detail taken on line 3-3 in FIG. 2showing vacuum breaking air channels and air escape ports.

FIG. 4 is a perspective view of the press platen of FIG. 1, removed fromthe machine and somewhat exaggerated in scale for better understanding.

FIGS. 5 and 6, respectively, are perspective views of press platens ofalternative forms.

The present invention anticipates that a platen, embodying the presentimprovements, is applicable, in its use, to presses of various designs,makes and mechanisms and it is not the intent that it be restricted tothe type of press which has herein been shown as being typical of pulppresses in general.

Before describing the present invention, attention will be directed tothe fact that, in the usual form of pulp press, both the top and bottomplatens have fiat and parallel bale engaging surfaces. A a result, thecellulose fibers in the bale are uniformly compacted since a uniformcompacting pressure is applied over the entire top and bottom surface ofthe bale, and as a result, air in the bale is trapped between thefibers. Since the bale is porous, the air will gradually escape and asit does, the fibers will bend to accommodate themselves to the spacesoriginally occupied by the compressed air.

It has been observed that with higher pressures and the increased speedof press closing, an increased length of retention period has beenrequired. Actually, a shorter over-all press cycle was obtained by aslower application of pressure that avoided air trapping.

The basis of the present invention resides in so designing the contourof the platen that it first comes in contact with the center of the balesurface as the press closes, subjecting the air contained therein at thecenter to a greater pressure than at the edges, thereby bringing about afaster outflow of air from the bale, due to the delayed compression ofthe fibers around the bale edges.

It will also be called to attention that, in the normal pressing by useof fiat surfaced platens, the center of the bale is apt to be leftslightly convex, unless an excessive retention period is allowed; thisby reason of compression of fibers about the bale edges while air isstill trapped or held in the bale center.

The designing of the present platen has been to reduce air trapping to aminimum and effect the progressive application of pressure to the balefrom center to to the outer edges thereof to expedite the outflow of airtherefrom.

Referring more in detail to the drawings.

The press, herein shown in FIG. 1, is typical of presses to which thepresent platen may be applied. It comprises a base frame structuredesignated, generally by reference numeral 10; an opposedly relatedupper structure 11 that is joined to and supported from the base framestructure by paired laterally spaced columns 1212, disposed in parallelrelationship. A cross-head 13 is slidably mounted on the columns 1212for movement toward and from the base frame. The base frame structure 10is horizontally disposed and mounts thereon a bale supporting platform10x upon which a pulp bale, designated at 14, is here shown to beproperly disposed for pressing.

The means supplying power for opening and closing the press is notherein shown in detail as it may be any suitable source. It is hereinrepresented as a hydraulic cylinder 15.

Fixed to the under surface of the cross-head 13 is a press platen 16embodying the improvements of the present invention. This platen, as hasbeen well shown in FIGS. 2 and 4, is of rectangular form, and hashorizontal dimensions that are preferably slightly greater than thedimensions of the top surface of the bale 14 to be pressed. The platenis fixed to the underside of the cross-head 13 in such position as tosymetrically engage the top surface of the bale incident to the closingof the press against the bale. The top surface of the platen is fiat andis seated flatly against and secured to the under surface of thecross-head 13 and it is formed from edge to edge of this top surfacewith a plurality of air escape channels 18 from each of which channels,air escape passages or holes 19 lead to the bale engaging surface of theplaten as best seen in FIG. 3; these holes being at relatively closeintervals over the platen surface.

An important feature of construction of this platen resides in thecontour of its bale engaging surface. It is shown in FIGS. 2 and 4 thatthe bale engaging surface is convex, both in its transverse and itslongitudinal direction. However, it might, in some instances be convexin one direction only, as has been shown in the modified or alternativeform illustrated in FIG. 5. It is also proposed that such platens mightalso be made with a flattened pyramidal bale engaging surface such asthat of the platen of FIG. 6. In this latter device, the pyramid hasbeen merged into a spherically curved tip, as designated by referencenumeral 20.

In the pressing of a pulp bale, in a press using the platen of FIGS. 2and 4, the problem of exhausting air long distances through the balethrough highly compressed fibers is accomplished. The same advantagesreside in use of the platens of FIGS. and 6 by reason of the progressiveapplication of pressure from the bale center outwardly.

The vacuum breaking details of the platens are not necessary to theoperation of exhausting air from the bale, but are necessary to asatisfactory commercial operation of the press. The combination of theplaten surface contour and the vacuum breaking features are quitedesirable in order to obtain a shorter retention period; a satisfactoryflat surface on the bale, and a satisfactory release of the pressed balein the opening of the press.

What I claim as new is:

A pulp bale press of the character described comprising a fixed meansfor support of a stack of pulp sheets or the like, a vertically movablemeans disposed for movement toward and away from said fixed means, and aplaten connected to the lower portion of said movable means, said platencomprising a unitary member having an upper surface and an opposed stackengaging surface, said surfaces being connected by side surfaces, saidupper surface being disposed adjacent the lower portion of said movablemeans, said stack engaging surface being generally convex with thethickest portion of the platen disposed at the central portion of theplaten and with the thinnest portion of the platen disposed alongperipheral portions of the platen so that the stack engaging surfaceinitially engages the top surface of a stack of pulp sheets at a medialpoint of the stack and progressively engages such top surface toward theperipheral edges of the top surface, said platen having a plurality ofair ports formed therethrough, the lower ends of each of said portsopening through said stack engaging surface, said upper surface havingformed therein a plurality of spaced air channels extendingsubstantially all the way across the upper surface of the platen, saidair channels opening through at least one of said side surfaces, theupper portions of each of said air ports opening into one of saidchannels with a plurality of air ports opening into spaced portions ofeach of said channels thereby providing communication between the lowerportion of said air ports at said stack engaging surface andatrnoshpere.

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